Roofs having a single-ply roofing membranes are so named to contrast them with another group of commercial roofing products known as built-up roofing. Built-up roofs are literally constructed on the roof by the contractor using component materials such as felts and asphalt. As such, they are subject to the problems caused by weather, worker error, and material inconsistencies. Single-ply membranes, however, are flexible sheets of compounded synthetic materials that are manufactured in a factory to strict quality control requirements that minimize the risks inherent in built-up roof systems. Primary among the many physical and performance properties these materials provide are strength, flexibility, and long-lasting durability. The inherent advantages of pre-fabricated sheets are the consistency of the quality of the products that are manufactured, the versatility in their attachment methods, and therefore, their broader applicability. They are inherently flexible, used in a variety of attachment systems, and compounded for long lasting durability and watertight integrity for years of roof life.
Single-ply roofing membranes can be categorized in technical terms as thermosets, thermoplastics, and modified bitumens. Thermoset membranes are compounded from rubber polymers. The most commonly used polymer is EPDM (often referred to as “rubber roofing”). Another potential thermoset material is neoprene, although this particular formulation is no longer widely used for roofing. Thermoset membranes are successful for use as roofing materials because of their proven ability to withstand the damaging effects of sunlight and most common chemicals generally found on roofs. The easiest way to identify a thermoset membrane is by its seams—it requires the use of adhesive, either liquid or tape, to form a watertight seal at the overlaps. Chlorosulfonated polyethylene (e.g., Hypalon®) is a unique material because it is manufactured as a thermoplastic, but over time, it cures to a thermoset. Hypalon materials are heat sealed by fusing the seams. Thermoplastic membranes are based on elastomeric polymers that can be processed as plastics. The most common thermoplastic is PVC (polyvinyl chloride), which has been made flexible through the inclusion of plasticizers. Thermoplastic membranes are identified by seams that are formed using either heat (i.e., RF welding or hot air) or chemical fusion (using solvent borne cements). The resulting seams are as strong or stronger than the membrane itself. Most thermoplastic membranes are manufactured to include a reinforcement layer, usually polyester or fiberglass, which provides increased strength and dimensional stability. Modified bitumen membranes are interesting hybrids that incorporate the high tech formulation and prefabrication advantages of single-ply with some of the traditional installation techniques used in built-up roofing. These materials are factory-fabricated layers of asphalt, “modified” using a rubber or plastic ingredient for increased flexibility, and combined with reinforcement for added strength and stability. There are two primary modifiers used today: APP (atactic polypropylene) and SBS (styrene butadiene styrene). The type of modifier used may determine the method of sheet installation. Some are mopped down using hot asphalt and some use torches to melt the asphalt so that it flows onto the substrate. The seams are sealed by the same technique.
Historically, roofing membranes were comprised of a scrim impregnated with a bituminous asphaltic or rubber based compound, wherein one side of the membrane was coated with a mineral filler like sand, talc, or fine gravel. The scrim is typically polyester fibers or fiberglass. In the case of polyester fibers they were typically woven and sized, or nonwoven and spun bonded. In the case of fiberglass the glass was usually woven and sized. The fiberglass industry points out that roofing membranes formed from polyester is more prone to burning as polyester will burn and glass will not. The polyester industry points out that fiberglass is inherently more friable, and the membrane will become hard and more subject to cracking. More importantly, glass is hydrophilic and can cause water to weep into the membrane and, therefore, shortens the working life. The coal industry, which supplies the bituminous materials, and the oil industry, which supplies synthetic bitumen, has addressed the flammability issue by including particulate and fibrous fillers, and nonflammable polymers like PVC. U.S. Pat. No. 4,458,043 describes particulate fillers as reinforcing fillers, such as carbon black, silica, zinc oxide, phenolic resin and magnesium carbonate, and non-reinforcing fillers such as calcium carbonate (whiting), barium sulphate, hydrated aluminum silicate, china clay, and magnesium silicate. Fibrous fillers include natural and synthetic fillers, such as mineral fibers, wool, cotton, polyester, nylon, glass, and blends thereof. A more complete list would also include those fillers that also reduce flammability, such as antimony trioxide, and brominated compounds. The most commonly employed rubber is ethylene propylene diene monomer (EPDM), which has excellent weatherability, and can be used with or without a scrim. Common thicknesses are 40 to 200 mils. Splices are often a solid rubber sheet that is spliced together at the job site, and applied using either an asphalt based adhesive, or a polyurethane. The EPDM is often formulated so that it will continue to vulcanize when exposed to direct sunlight. A problem with a continuous curing system is that there will be shrinkage as curing continues, however, and as the EPDM cures it becomes more difficult to splice, because it is difficult to adhere to, except at high temperatures.
To solve the adhesion problem with vulcanized EDPM rubber, roofing membranes commonly have a backing laminated to the EPDM. This backing is commonly referred to as a fleece in the roofing industry. The fleece creates a surface that is easily adhered, and also adds dimensional strength. Fleece, in this context, is substantially a fuzzy scrim, felt or non-woven. The Carlisle Corporation manufactures a fleecebacked EDPM. The product and method of manufacture is described in U.S. Pat. No. 5,620,554. In a continuous process, a first side of roll stock of EPDM is abraded, passed through a rinsing vat filled with water and/or other cleaning fluids, and between a pair of counter-rotating cylinders covered with stiff-bristled nylon brushes that effectively remove any talc or other non-stick coatings from the vulcanized sheet, heated to a range of 250 to 350° F., and laminated to a polyester fleece matting with an intervening filmic polymeric adhesive forming a composite material. During lamination the polymeric film is melted, thus causing the matting to adhere to the first side of the cleaned, heated rubber stock. Typically, a selvage width on either side of the fleece is primed, and then laminated to a double-coated pressure sensitive tape having a release liner. The double-coated tape is to be used as a means for making a butt-splice with an adjoining roofing membrane. A problem with a splice using a double-coated tape is that there will frequently be adjoining membranes that do no have a selvage width that can be co-joined, and tape will either have to adhere to the un-abraded side of the EPDM roofing membrane, or some fastening system, such as one that adheres to the fleece and the un-abraded side of the EPDM roofing membrane, will need to be employed. In any case, the properties that contribute to the good weather resistance of EPDM rubber make splicing difficult. RF welding or solvent etching, for instance, as is used to join thermoplastic materials is problematic because cement solvents tend not to dissolve, but just to swell the EPDM rubber. Most EPDM membrane rubber is not thermoplastic, and does not facilely flow when heated, and has a low surface energy making EPDM rubber difficult to adhere to.
In an unrelated industry, Lin-Luc Jacques Servais Oosterlynck, disclosed in U.S. Pat. No. 3,695,962 a prior art Method of Making Pile Fabrics, wherein a fibrous layer is needle punched through a support fabric, whereby the needle punched fibers form tufts extending from the support fabric. The fibre tufts are then fixed in a position substantially normal to the support fabric, which is then stripped away from the fibrous layer. The fixing of the fibre tufts may be accomplished by a heat treatment or by a suitable chemical treatment. The resulting pile fabric is typically a carpet, or a velour. Of interest is that by backside needling, U.S. Pat. No. 3,695,962 discloses a process where the height of the pile can be tightly controlled.
What is desired is a single-ply roofing that is easily seamed at the job site that has excellent weather resistance, and that has excellent adhesion to roofing cements.